Well you need to come see me of course!

I totally agree about stopping at Buc-ee's though - definitely an I-10 must-see. Keep an eye out for their billboards along the way too - they're rather entertaining, haha.
If you're into sweets at all,
Crave Cupcakes in Houston is amazing. It's one of our must-stops whenever we go there.
San Antonio of course has the Riverwalk, Alamo and all that jazz. Although I'd say the mexican food is really the highlight around here. But then, we love food, haha. If you're looking to try Texas BBQ, our favorite is Coopers in New Braunfels which isn't too far off of I-10. It's only about 15-20 minutes from the east side of San Antonio to there on I-35.
West of San Antonio to El Paso is a LONG drive and there's really not a whole lot out there. Are you guys planning on driving through or are you looking to stop along the way? We drove all the way from San Antonio thru El Paso to Albuquerque in one day so you could definitely push through if there wasn't anywhere you wanted to stop. Then you could spend more time in the more eastern part of Texas where there's more to see.